Biology – MCAT Question of the Dayhttp://mcatquestionoftheday.com
Keeping your mind sharp for the MCAT, one question at a time!Thu, 21 Mar 2019 11:00:50 +0000en-UShourly1Switch Hitterhttp://mcatquestionoftheday.com/biology/switch-hitter/
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Which one of the following molecule is amphipathic, with both a hydrophilic and hydrophobic region?

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Correct Answer: B.Phospholipids

The cell membrane is composed of a phospholipid bilayer that has a hydrophilic head (where the polar phosphate is attached) and a hydrophobic tail (made up of hydrocarbon chains). Starch is a polysaccharide that is generally hydrophilic and can be dissolved in water. Triglycerides, steroids and cholesterol are all entirely hydrophobic not being able to be dissolved in water. The molecule mentioned in the question is both hydrophilic and hydrophobic, indicative of the phospholipid, therefore only answer option [B] is correct.

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]]>http://mcatquestionoftheday.com/biology/switch-hitter/feed/0Layer of the Epidermishttp://mcatquestionoftheday.com/biology/layer-of-the-epidermis/
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Which layer of the epidermis is the characterized by a low rate of mitosis and a high concentration of keratin?

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Correct Answer: C.Stratum corneum

If a layer of epidermis has a low rate of mitosis, this indicates that the cells in this layer are not dividing very frequently. Likewise the presence of keratin, signals that the layer of epidermis must have a waterproofing function. The stratum basale is the most mitotic layer and is the bottom layer of the epidermis. As the cells are produced in the stratum basale, older cells are pushed up to the stratum spinosum, which is also high in mitotic activity. Keratin dominates in the stratum corneum, which is the most superficial layer of the epidermis, characterized by dead skin cells that are no longer undergoing mitosis. Therefore, the correct answer is [C].

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]]>Otter Futurehttp://mcatquestionoftheday.com/biology/otter-future/
Fri, 18 Jan 2019 11:00:41 +0000http://mcatquestionoftheday.com/?p=4785Warning: sizeof(): Parameter must be an array or an object that implements Countable in /home/xipgqzel/public_html/mcatquestionoftheday.com/wp-content/plugins/php-code-for-posts/PHPPostCode.php on line 544

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In a small lake, sea urchins graze upon small grasses that grow on the bottom. After the introduction of an exotic sea urchin, the small grasses became over grazed and absent. To solve the problem, a species of otter is introduced into the lake to predate upon the sea urchins, and the balance between the urchins and sea grasses is restored. What would be the appropriate term for the otter that was introduced?

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Correct Answer: C.keystone predator

The otter would be considered a SECONDARY consumer, the urchins are the primary consumers, and a hypothetical predator of the otter would be a tertiary consumer. Since the otter is responsible for preventing overgrazing of the small grasses by predating on the out of control urchin population, it is termed a keystone predator that exerts a “top-down” effect on the ecosystem.

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]]>Favored Reaction in Thermodynamicshttp://mcatquestionoftheday.com/biology/favored-reaction-in-thermodynamics/
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According to the second law of thermodynamics, which of the following reactions would be favored?

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Correct Answer: C.2H2O2 -> 2H2O + O2

The second law of thermodynamics states that nature tends to favor a state of disorder or entropy. In other words, chemical reactions that are exergonic (release energy) and result in more products than reactants are favored. The only answer option that has more products formed in comparison to the reactants is answer option C.

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]]>Primitive Atmospherehttp://mcatquestionoftheday.com/biology/primitive-atmosphere/
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According to scientists, Oparin and Haldane, which of the following gases were present in the primitive atmosphere?

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Correct Answer: A.CH4, NH3, H2, H2O

In the primitive atmosphere, no O2 was present as most organisms used chemosynthesis to create organic compounds. The Oparin and Haldane hypothesis states that methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O) were the only gases present. It was after the Miller and Urey experiment that it was proven that these gases and lightning could have given rise to simple organic compounds that then later evolved into more complex forms of life.

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]]>Catalyzing Chemical Reactionshttp://mcatquestionoftheday.com/biology/catalyzing-chemical-reactions/
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Enzymes are one of the key proteins in cells and facilitate chemical reactions. How does a typical enzyme catalyze a chemical reaction?

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Correct Answer: B.It reduces activation energy of a chemical reaction

Enzymes reduce the activation energy of chemical reactions by binding substrate(s) into energetically favorable orientations. They greatly reduce the activation energy, but do not eliminate it completely. Enzymes are completely reusable—they do not participate in the reaction as a substrate. Even when cofactors are needed for the successful action of the enzyme and though they may be tightly bound, they are not covalently bound to the enzyme. Enzymes do not add additional energy to chemical reactions as heat would, for example.

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]]>Cerebrospinal Fluid Producershttp://mcatquestionoftheday.com/biology/cerebrospinal-fluid-producers/
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Cerebrospinal fluid (CSF) is created by special capillary networks located in the brain. CSF bathes the hollow regions of the brain, spinal cord, and around the central nervous system, within its protective coverings. The areas that the CSF pathway includes are:

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Correct Answer: A.the ventricles, spinal canal, and meninges.

The organs of the central nervous system (CNS), the brain and spinal cord, have hollow regions (ventricles and spinal canal, respectively). The CNS also contains the meninges, which consists of three layers of protective covering. The question states that CSF circulates in these areas. Thus A is the correct answer. The spinal nerves and cranial nerves are not part of the CNS, they are part of the peripheral nervous system (with the exception of cranial nerve II, but that’s a little advanced for the MCAT).

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]]>Nerve Impulse Propagationhttp://mcatquestionoftheday.com/biology/nerve-impulse-propagation/
Mon, 12 Nov 2018 11:00:43 +0000http://mcatquestionoftheday.com/?p=4193Warning: sizeof(): Parameter must be an array or an object that implements Countable in /home/xipgqzel/public_html/mcatquestionoftheday.com/wp-content/plugins/php-code-for-posts/PHPPostCode.php on line 544

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The velocity of nerve impulse propagation could be increased by:

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Correct Answer: D.A and C

During the evolution of living systems, there were two ways the velocity of nerve impulse propagation could be increased. The first way was increasing nerve diameter, while the second way was the formation of the myelin sheath. The latter mechanism is less energetically expensive than the former.

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]]>Gastrin Secretionhttp://mcatquestionoftheday.com/biology/gastrin-secretion/
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Which of the following statements is NOT true regarding gastrin secretion and function?

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Gastrin stimulates parietal cells to release HCl. If A were true, then there would be a positive feedback loop where gastrin is stimulating more HCl production, and HCl is stimulating more gastrin production, causing us to burn a hole through our stomach! Increased production of HCl by parietal cells leads to somatostatin secretion, which inhibits the secretion of gastrin. Lastly, an elevated gastric pH (i.e. low amount of acid) would stimulate the G cells to release more gastrin in an attempt to stimulate the parietal cells to release more HCl to bring the acidity back to normal.

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]]>Decreasing Activity of an Enzymehttp://mcatquestionoftheday.com/biology/decreasing-activity-of-an-enzyme/
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Some enzymes experience a decrease in activity proportional to the concentration of their products. This phenomenon could be an example of what process?

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Correct Answer: D.Both A and B

Many cellular enzymes exhibit decreasing activity with increasing levels of reaction product. This feedback inhibition help regulate the activity of enzymatic processes. Often this process occurs through non-competitive inhibition. The product of the chemical reaction binds to the enzyme in a location other than the active site, which causes a conformational change in the enzyme and decreases enzymatic activity. Allosteric activation describes a process in which enzymatic activity is increased because of binding of some molecule to a site other than the active site.